1. Field of the Invention
The present invention is directed to a circuit for an infrared detector, and in particular to such a circuit having a field effect transistor connected to a gate resistor.
2. Description of the Prior Art
One of the critical demands made of infrared detectors is low noise. In known circuits for operating such infrared detectors, noise voltages are generated by several sources. Such circuits having a high-impedance gate resistor, which may be formed by a diode, which constitutes a source of noise voltage. Additionally, the field effect transistor has a gate leakage current which results in a voltage drop at the gate resistor (resistance noise), and the transistor also generates channel voltage noise.
Although the magnitude of the resistance noise cannot be influenced, the frequency or phase behavior of the noise can be shifted by using pyroelectric materials having high capacitance. It is thus important to consider the correct parameters in the selection of the field effect transistors which are used. Gate leakage currents as small as one picoampere may result in a noticeable increase in the noise voltage.
Among semiconductor components, field effect transistors are in a class of such components which are particularly sensitive to voltages. Because excessive temperature stresses on the components during manufacture, storing and manipulation cannot always be avoided, such stresses can result in the generation of charges both by the pyroelectric effect of the materials, and the piezoelectric effect during mechanical stressing. Such charges can easily elicit voltages above the gate punch through voltages. A transgression of this gate punch through voltage can cause defects at the pn junction of the field effect transistor which in turn increase the gate leakage current both as a chronological average and in the occurrence of peaks. This results in an increase in the overall noise.